Energy dependence of anisotropy of defect production in electron irradiated diamond-type crystals

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Abstract
Studies are reported of damage rate deduced from room-temperature conductivity measurements on n- and p-type floating zone silicon samples ∼ 20 μ thick, subject to electron irradiation at energies from 0·3 to 2·0 mev. For the n-type material, each specimen was cut to an orientation such that, by rotating the specimen, successive irradiations could be given along a chosen pair of crystallographic directions making equal angles with the specimen face. The results show repeated crossing over of the damage rate versus energy curves for different orientations. With increasing energy, the beam direction giving the highest rate changes from ⟨111⟩ to ⟨110⟩ to ⟨100⟩ to ⟨111⟩ in this range. Arguments are presented that the carrier removal rate depends almost entirely on the introduction rate of single primary defects. A correction is applied to our earlier published results following Stein's recent work, and agreement on the sequence of orientation effects is then found with the present measurements. On p-type material, in separate irradiations at normal incidence on oriented specimens, slight annealing and a lower carrier removal rate are seen; the orientation and energy dependence are similar to n-type up to ∼0·7 mev, above which a steeper energy dependence and highest damage rate along ⟨100⟩ up to ∼ 1·9 mev are attributed to the creation of significant numbers of primary divacancies.